a) Field of the Invention
The invention is directed to a method and an arrangement for determining the spatial coordinates of at least one object point through video measurement image tachymetry, preferably for use in geodesy and also in building surveying and object surveying.
b) Description of the Related Art
Modern electronic tachymeters have an arrangement for automatic fine target seeking. In the first step, assuming the presence of image evaluation electronics, they would enable the storage of the target image for supplementing the measurement data of the tachymeter comprising the distance to the target point marked by a reflector, the horizontal angle and the vertical angle. The entire surrounding field of the measurement point can accordingly be fixed in the digital image. This would be the video tachymeter in its simplest form. The precondition for this is that the object field or the object is located, in the horizontal direction, virtually vertical to the optical axis of the video tachymeter and that all objects appear simultaneously sharp in the target image. Likewise, the sighting must be virtually horizontal.
An arrangement of a xe2x80x9cvideo tachymeterxe2x80x9d is indicated in DE 36 28 350. In this reference, the reflector is photographed by a video camera arranged on a tachymeter with a point number label to supplement the measurement value of the tachymeter with the added information, that is, the point number. Thus, in this case, additional information is collected which is only used to improve documentation of the terrain points to be measured. Measurements of the terrain points based on the recorded images are not possible with this arrangement.
DE 198 00 336 shows another simple arrangement with an entirely different purpose. In this case, a sensor measuring unit for measuring distances is located on the camera. Data for the orientation of the camera to the object are collected by this arrangement and employed digitally. The measurement values of the camera accordingly maintain an absolute orientation.
WO 97/36147 is likewise directed to the orientation of a video camera to a scene as an object with three selected points whose position is known. Data from the recorded images are used for determining the position of the camera.
DE 196 04 018 is directed to an entirely different object. The arrangement comprises a theodolite with a target pointer and a laser beam distance meter mounted thereon for distance measurement without reflectors. The distance to the surface of the object is measured and the edges of the same are sighted with the telescope, and the angular position of the object is determined. The width of the object can be calculated from the distance and the angle. This reference does not concern a video tachymeter. Measurement values of the object are calculated from the determined measurement data of the theodolite and distance meter by means of a computer. A recording of an image of the object to be measured and determination of measurement data of the object from this image are not carried out.
In EP 0 417 125 B1 (DE 689 04 911 T2), the correlation of three point with surfaces of rooms or spaces is determined with a similar arrangement via these three points by measuring distances and angles. When a plurality of surfaces are measured, lines of intersection and corner points can be determined depending on the quantity of measured surfaces. Here also, no images of the room to be measured are recorded and no measurement data are obtained therefrom.
Arrangements for distance measurement and focusing in photographic cameras do not satisfy the strict requirements for accuracy in geodesy.
In the informational publication xe2x80x9cSurveyor(trademark) ALS with Video Optionxe2x80x9d by the company MDL, a terrain image of an object in the form of terrain is digitally composed from spatially oriented and positioned video pictures by means of a digital video camera and measurement is carried out by means of polar data (distance and angle) which are determined by a normal tachymeter. This digital terrain image has plan information and height information; the latter is determined, and then displayed, in the form of contour lines by means of geometric calculation as is conventional in the making of plans and maps. Dimensional calculations and terrain models can then be derived with the help of these data. Since a distance meter without reflectors is involved, according to this publication, open terrain can be surveyed from an elevated viewing point or stand point without inspection on foot. This is an advantageous application variant of video tachymetry. Unfortunately, it has only very limited accuracy.
To summarize, it can be stated that in the cited prior art:
no measurements are carried out in the video image,
there is no combination of the video image data with the data of the tachymeter and/or theodolites such as distances, horizontal angles and vertical angles,
no data are derived from these direct measurement data,
and no video tachymetry is undertaken.
The object of the EV consists in obtaining and utilizing measurement data from the stored target image for determining additional object points. For this purpose, a plurality of base points marked by reflectors are determined in the video image, wherein distances and angles relative to these base points are measured centrically subsequently in order to determine measurement points between the marked base points from the measurement data of the video image during a subsequent home evaluation of the measurement data and measurement images. At great distances, all images appear sharp almost simultaneously. In order to detect the marked object point in a sharp surrounding area at shorter sighting distances at which the objects extend depthwise, transformation is carried out on this image with maximum contrast proceeding from the images of the base points. In this way, an accurate marking of the desired object point is possible. For this reason, the digital image must have the quality of a measurement image. Because of this possibility, it is possible when recording the terrain to limit to a few critical points which simultaneously form the base points in order to determine additional object points from the video image during the homebase working phase, the positions of these object points being derived computationally from the base points. These object points can be marked during the recording as well as afterwards in the video image by means of a mouse. This possibility saves time when recording in the field and it permits the spatial recording to be supplemented without subsequent footwork or additional field comparison.
Accordingly, it is the primary object of the invention to provide a method and an arrangement for video measurement image tachymetry by which measurement data can be obtained from the recorded target image for effectively determining the position of object points and which reduces expenditure on geodetic measurements.
According to the invention, this object is met by a method for determining the spatial coordinates of at least one object point Pi from the coordinates of at least two base points which serve as reference points and which do not lie in a plane by a video tachymeter which is arranged at a recording stand point, is swivelable about a vertical axis StA and comprises a distance measuring arrangement, a video camera with CCD matrix, a sighting device and angle measuring devices, wherein the video camera is tiltable about a horizontal axis. The method includes the steps of marking the base points B1; B2 in the terrain and sighted by the sighting device, measuring their coordinates by the distance measuring arrangement and angle measuring devices, additionally recording a target image Mxe2x80x21; Mxe2x80x22 containing the marked base points B1; B2 and the object points Pi by the video camera and storing the target image and determining the coordinates of the object points Pi from their image point coordinates in the target images Mxe2x80x21; Mxe2x80x22 and from the base points B1; B2 which are marked and determined by tachymetry.
Also in accordance with the invention, an arrangement for determining the spatial coordinates of at least one object point comprises, at the measurement stand point, an electronic tachymeter with an automatic sighting device and a transmitter. The electronic tachymeter is swivelable about a vertical axis (StA). A distance measuring arrangement is included which is tiltable about a tilting axis KA. Also included are a video camera with a CCD matrix, a sighting device and angle measuring devices for measuring horizontal and vertical angle. At the target point, a sighting rod with reflector, a radio device, a receiver, and a graphic field book with storage components are provided. At least a portion of the beam path of the distance measuring arrangement is arranged coaxial to the optical axis of the video camera. A tube is provided for focusing the CCD matrix of the video camera. The tube is controllable depending on the distance measured by the distance measuring arrangement or adjustable manually in direction of the optical axis according to the sharpness or contrast of the video image. An image processing system is provided for detecting object points and their specifying as object points with a determined position.
Accordingly, it is advantageous when the marking of the base points that are determined by tachymetry is carried out in the recorded target images.
In order to facilitate the measurement of object points and to reduce outside field work, the selection of object points Pi to be measured at the target point is advantageously carried out in a target image transmitted to a screen provided at that location or is carried out subsequently during home processing with the aid of recorded and stored target images.
The following method steps are advantageously provided in a method for determining the spatial coordinates of at least one object point Pi from the coordinates of at least two base points which serve as reference points and which are determined by means of a video tachymeter which is arranged at a recording stand point, is swivelable about a standing axis StA, and provided with a receptacle for a distance meter, this receptacle being tiltable about a horizontal tilting axis, with a video camera with CCD matrix, with a sighting device and with angle measuring devices:
sighting of two base points located in the object space through the video tachymeter which is arranged at a recording stand point and is rotatable about a standing axis by a horizontal angle, this video tachymeter having a video camera that is tiltable about the horizontal tilting axis, and determining the oblique distances to the at least two base points by means of the distance measuring arrangement of the video tachymeter,
producing two video images containing the at least two base points and storing of the same, wherein the camera is oriented in such a way that the image of the respective sighted base point lies in the respective principal point of the objective of the video camera,
the x-, y- and z-coordinates of at least one searched object point located in the space encompassed by the video images and marked during the recording or marked on the recorded video images by means of the target image coordinates measured in the target images for the selected object point that is situated in the object space and imaged on the CCD matrix of the video camera are determined from the oblique distances to the base points, from the measured horizontal angle, from the vertical angles to the base points, from a device constant and from the focal length of the objective, wherein these coordinates x, y, z are coordinates of a coordinate system with axes X; Y; Z with their coordinate origin lying at the intersection of the tilting axis and standing axis of the video tachymeter, and the standing axis extends vertical to the X-Y plane and determines the direction of the Z-axis.
The method is advantageously carried out in the following method steps:
a. Sighting a first base point by adjusting the axis of the video camera at a first horizontal angle and at a first vertical angle relative to the X-Y plane in the direction of the first base point and measuring of the first vertical angle and the first horizontal angle, wherein the vertex of this vertical angle and of the horizontal angle lies in the tilting axis of the video tachymeter; recording and storing a first target image and measuring the oblique distance to this first base point with a distance measuring arrangement arranged coaxial to the axis of the video camera of the video tachymeter, wherein the video camera is oriented in such a way that the image of the first base point lies in the principal point of the objective of the video camera and, further, contains the image of the second base point.
b. Swiveling the video tachymeter about a second horizontal angle formed by the two base points and the standing axis of the video tachymeter, wherein the vertex of this angle is located on the standing axis;
c. Sighting a second base point by adjusting the axis of the video camera at a second horizontal angle and at a second vertical angle relative to the X-Y plane in direction of the second base point and measuring the second vertical angle and second horizontal angle, wherein the vertex of this angle lies in the tilting axis of the tachymeter, recording and storing a second measurement image and measuring the oblique distance to this second base point with the distance meter of the video tachymeter, wherein the video camera is oriented in such a way that the image of the second base point lies in the principal point of the objective of the video camera and, further, contains the image of the first base point.
d. Determining the coordinates of any object points contained in the recorded target images and located in the object space by means of the coordinates of the first and second base point by
da. marking the searched object point during recording in the present video image or marking the searched object point in the recorded video images by means of clicking on a mouse;
db. measuring the target image coordinates of the object point in the recorded video images or recordings;
dc. converting the target image coordinates of the object point which are located in the respective plane of the CCD matrix into analog coordinates located in the object space by means of
the measured oblique distances to the two base points, corrected by the device constants,
the measured target image coordinates,
the focal length of the objective of the video camera,
dd. calculating parameters of needed support points by means of
image coordinates of the target images converted in the object space
the measured oblique distances to the two base points,
the measured horizontal angle by which the video tachymeter must be swiveled about the standing axis during subsequent sighting of the base points,
the measured above-mentioned vertical angles relative to the base points,
distances which are derived from the horizontal angle, from the above-mentioned oblique distances and from the two vertical angles,
de. transforming these support point parameters into the coordinates of the coordinate system X; Y; Z with its origin at the intersection of the standing axis and tilting axis and determining the coordinates of these support points in this coordinate system.
e. Calculating the coordinates x; y; and z of the object point with the coordinate origin of said coordinate system which lies in the intersection of the tilting axis and standing axis of the video tachymeter by means of the coordinates of the said support points by determining the coordinates of the intersection of two straight lines g1 and g2 defined by these support points. The coordinates of this intersection are also the coordinates of the object point to be measured.
To continue a video image traverse started at a first stand point of the tachymeter with a traverse comprising object points proceeding from a second tachymeter stand point, the traverse comprising object points is determined proceeding from the first stand point of the tachymeter and is continued proceeding from the second stand point of the tachymeter.
According to a further realization of the method according to the invention, particularly when the additional object point lies in another focal plane, which can quickly become the case with short sighting distances and the observer must refocus on this plane and clearly mark the desired object point, it is advantageous when an image evaluating device determines the target image coordinates of the desired object point that belong to a desired object point plane, after which focusing is carried out in the target image planes of the object points by means of an autofocusing device. The image evaluating device for detecting object points and their specifying as object point with a determined position is carried out by means of a transformation of known target image planes to a plane of this kind with maximum contrast.
An arrangement for determining the spatial coordinates of at least one object point comprises, at the measurement stand point, an electronic tachymeter with an automatic sighting device and with a transmitter and, at the target point, a sighting rod with reflector, receiver and the graphic field book with storage components. The electronic tachymeter or video tachymeter is swivelable about a vertical axis and comprises a distance meter which is tiltable about a tilting axis and a video camera with a CCD matrix. The video tachymeter further comprises a sighting device and angle measuring devices for measuring horizontal and vertical angles. In this connection, it is advantageous when at least a portion of the beam path of the distance measuring arrangement is arranged coaxial to the optical axis of the video camera, when a focusing arrangement is provided for focusing the CCD matrix of the video camera, this focusing arrangement being controllable depending on the distance measured by the distance measuring arrangement or adjustable manually according to the sharpness of the video image, and when an image processing system is provided for detecting object points and their specifying as object point with a determined position.
The CCD matrix of the video camera is advantageously arranged in a tube which is displaceable in a controllable manner in direction of the optical axis for purposes of focusing, its displacement being realizable by a drive unit which is controlled by computer according to an algorithm.
Accordingly, it is further advantageous that the respective displacement path of the CCD matrix is calculated by the computer corresponding to the distances from the respective sighted base point that are determined by the distance measuring arrangement.
It is further advantageous when an image evaluating device controls an autofocusing system in such a way that the focusing position of the CCD matrix pertaining to a selected object plane measures target image coordinates of the desired object point Pi, wherein the base point B1 and B2 whose images Bxe2x80x21 and Bxe2x80x22 lie in the target image planes Mxe2x80x21 and Mxe2x80x22 must be sighted. The displacement path can also be derived in this case during the focusing of the CCD matrix from the object point plane located between the target image planes of the base points by an image transformation toward the maximum.
The sighting rod located at the target point comprises a signal receiver or data receiver and a computer with a target image screen, so that all operations can be carried out at the target point in the same way as at the stand point.
The method includes progressive measurement point marking in the target images at the target point, control of the measuring process and the methods of determining the selected object points from the measurement data of the tachymeter and its camera. The determination of the positions of the object points in all three coordinates form two measurement points is only possible according to the invention in that additional support points are derived from the tachymeter data and video image data, so that intersecting straight lines can be formed therefrom, the intersections of these straight lines representing the selected object points with their coordinates. The tachymeter reference points can also be marked by a laser pointer and the distances can be measured without reflectors. The horizontal angle and vertical angle are indicated in a known manner with the sighting. The marked reference or base points are highlighted by the laser light in the video image. The correlation of the images is given by the indicated angles.